how much driving to recharge battery

Submitted: Tuesday, Apr 02, 2013 at 12:03
ThreadID: 101428 Views:3011 Replies:13 FollowUps:6
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I know that this is a 'how long is a piece of string' question but we will be traveling through the west and centre for a few months and running a 40 litre engel off a deep cycle battery. Because we have young kids we won't be doing super long days, in fact in the Pilbara and Kimberley we will often stop for a few days then drive about 4 hours to our next stop for another few days. I know from previous experience that the battery will happily run the fridge for 5 days if we are careful, but I am concerned that we will not be driving for long enough to fully recharge the battery. So, any thoughts on whether I should also invest in a folding solar panel or am I being overly cautious? The Minister for finance won't be happy if we need the panel but I can hide it in the back until we reach our first campsite.
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Reply By: rocco2010 - Tuesday, Apr 02, 2013 at 12:40

Tuesday, Apr 02, 2013 at 12:40
Gidday Prof

I don't know how long it takes to charge a battery but I reckon the fact that you asked this question means you know you need a solar panel.

It is probably easy for me because the Minister for Finance and I had a fundamental disagreement a few years ago and she has not been replaced. I now rule as dictator and the finances of the kingdom, particularly when it comes to expenditure of this nature, are much improved.

But in the interests of united goverment, i would call a special cabinet meeting (that means a nice dinner) and use that opportunity to point out to the Minister that if the battery goes flat out in the sticks there won't be any nice dinners.

I know budgets can be tight but if you are going to be away for an extended period the cost of the panel will be probably be a small extra on top of what you have already spent and will spend. And you can't put a price on peace of mind. When it's two days drive to the shop you don't want to be worrying about the fridge.

Enjoy your travels


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Reply By: baz&pud (tassie) - Tuesday, Apr 02, 2013 at 12:50

Tuesday, Apr 02, 2013 at 12:50
I was told once that if you drive for three to four hours that will recharge your battery, but if it's dead flat I wouldn't think that three hours would be enough.
Suggest you discuss with the Minister about purchase of at least a minimum 80watt solar panel, but bigger if the Minister will allow the expense, don't purchase and hide till the first camp site, been there done that, take it from a grey nomad that knows.
Enjoy your trip.
Go caravaning, life is so much shorter than death.

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Reply By: Ross M - Tuesday, Apr 02, 2013 at 13:04

Tuesday, Apr 02, 2013 at 13:04
G'day Prof
5 days running and Engel if your careful?
You must be mighty careful or the ambient is cool or both.

Up in the Kimberley where it is hotter and the vehicle will be in that heat too means the ambient in the car might often be 40 or more.

In similar circumstances my Engel will run about 18 or more hours per day cos it is also hot at night too.
Before a 50% discharge is reached you possibly will have only a day and a half.
Then you can only charge an AGM at about 20 amp max and when they are already warm t should be less amps or the battery will suffer and early demise. Therefore the length of time for charging increases.

The engine/alternator will replace the majority of power in a couple of hours but for a full charge it will take quite a while because of the way charging occurs.
Solar will help to keep it topped up when stopped.

Ross M
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Follow Up By: Prof Stick - Tuesday, Apr 02, 2013 at 13:54

Tuesday, Apr 02, 2013 at 13:54
Refrigerate/freeze food before you go. Charge spare battery with 240V charger. Only open when necessary and yep have had 4 days in mid-north coast summer.
might be different up there though :(
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Apr 02, 2013 at 16:35

Tuesday, Apr 02, 2013 at 16:35
Hi Prof,
"Mid-north coast"?? I take it you mean of NSW??
You've not been to Pilbara and The Kimberley before have you?
Yes, it is "different".

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Reply By: Member - John and Val - Tuesday, Apr 02, 2013 at 13:50

Tuesday, Apr 02, 2013 at 13:50
Hi Prof,

I can almost guarantee that in the Kimberley heat (yes, even in mid winter its hot up there) your wife will not begrudge the cost of a solar panel, as it will surely mean the difference between cold or spoiled food and drinks.

Suggest that you have a look at our Electricity for Camping blog click here to get an understanding of what is involved.


J and V
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Follow Up By: dbish - Tuesday, Apr 02, 2013 at 13:54

Tuesday, Apr 02, 2013 at 13:54
The sudden apearence of a new solar pannel may result in Cold shoulder & Hot tounge for the rest of the trip. Best get it sorted before trip. But i would definitly go for the pannel, at least if you finish up traveling alone the beer @ food will be cold, good luck.
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Reply By: Prof Stick - Tuesday, Apr 02, 2013 at 13:51

Tuesday, Apr 02, 2013 at 13:51
Thanks guys. So if I follow the appropriate protocols (dinner, nice wine etc.) and am ready to make a submission, how high do I go? I just rang a couple of retailers and both tried to convince me that anything less that 120W was futile but I am suspicious they just want to sell me the biggest system they have. Will 80W keep me topped up or do I need 120? Remember its a 40L Engel.
AnswerID: 508018

Follow Up By: Member - John and Val - Tuesday, Apr 02, 2013 at 13:59

Tuesday, Apr 02, 2013 at 13:59
Hi again,

The size of panel required will depend on, among other things, your electricity usage patterns. Before you rush out and buy something please take the time to read that blog - then you will be able to work out what YOU need without relying on sales people who just want to make a sale. Happy to help with more specific questions after you have worked out your particular needs.


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Reply By: rooster350 - Tuesday, Apr 02, 2013 at 13:55

Tuesday, Apr 02, 2013 at 13:55
140w folding solar panel with regulator and delivered , on Ebay costs $195...with no ongoing then should not have to worry to much about your lack of power to keeps things cold...cheers
AnswerID: 508019

Follow Up By: Member - Grundle (WA) - Tuesday, Apr 02, 2013 at 19:50

Tuesday, Apr 02, 2013 at 19:50
Hi Rooster,any idea of the quality of those.Ta

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Follow Up By: rooster350 - Tuesday, Apr 02, 2013 at 20:52

Tuesday, Apr 02, 2013 at 20:52
A friend of mine in Ballarat bought one last week and he is quite pleased with it, does the job...cheers
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Reply By: Michael ( Moss Vale NSW) - Tuesday, Apr 02, 2013 at 18:44

Tuesday, Apr 02, 2013 at 18:44
We have a very power thirsty 90 litre fridge, we also have a roof tent so its not practical to pack up every day to drive to charge the batteries. We run the Patrols engine every afternoon if we haven't been on the road that day for 30 minutes, slightly above idle and that is sufficient to charge the two N70ZZ batteries that are connected in parallel. Also if we are bush camped we take the opportunity to use our onboard shower at the same time as the vehicle is up to running temperature. We cant notice any difference in fuel consumption using this system. A 40 litre Engel fridge should be fairly easy to manage. Michael
Patrol 4.2TDi 2003

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Reply By: Member - Russler - Tuesday, Apr 02, 2013 at 20:28

Tuesday, Apr 02, 2013 at 20:28
Guess you need to work on how you sell it ... eg. does the GLW like cold soda water in her GnT? Need to emphasis the 'cold' bit, and obviously it's horses for courses, ie. soda water in the GnT may not be her thing, but there must be some angle you can work. We went to The Kimberley in July/Aug 2000, and it was hot. We're going again in September this year, so it'll be hotter. Consequently we've invested in 80W of solar panels to help top up the aux battery. Good luck :)
AnswerID: 508049

Reply By: Member - Derek Y1 - Tuesday, Apr 02, 2013 at 23:06

Tuesday, Apr 02, 2013 at 23:06
Have you considered a 12v-12v charger for your battery setup.
Supposed to FULLY charge AGM batteries in a fraction of the time taken by the alternator.
We have one installed in our 200 'Cruiser and it seems to have worked out OK.
Some of the chargers can't be installed under the bonnet though due to heat.
Ours is in the back along with the AGM battery.
Korr Lighting had a 165w solar system on special at Brisbane 4WD show recently.

Best of luck

AnswerID: 508059

Reply By: The Bantam - Tuesday, Apr 02, 2013 at 23:54

Tuesday, Apr 02, 2013 at 23:54
How long your battery will take to charge WILL depend on how deeply it is discharged...of course.

Then there are the compliactions of type and age.....the older the battery the slower it will charge.

Remember too the battery will recover a large portion of its charge very quickly form a high capacity charger like a car alternator.......its that last portion to "fully charged" that takes the time.

As the battery "fills with charge", the charge rate slows.

Some people get paranoid about having the battery"fully charged".

A deeply discharged battery may take 6, 8 hours or more to "fully recharge" and there is nothing you can do about that and no facncy charger will change that much.

I have had batteries that have been deeply discharged take over 24 hours to "fully charge".....on smart chargers.

Running a fridge till the battery is deeply discharged is not good for the battery.......ya battery may run the fridge for 5 days......but it wont be happy.

A solar pannel is a realy good idea, even if it does not "keep up" with the demand, it will dramaticaly increase the run time on battery and significaly reduce the wear & tear on the battery.

I was reading a reasearch paper on batteries the other day, & they reconed the life of a battery in a stationary application could be reduced from the designed 15 years to 60 days by repeated deep discharge and higher ambient temperature.....and they where talking as few as 10 deep discharges and the sort of temperature commonly found under bonnet.

The most imporatant thing is not allowing the battery ( any battery) to become deeply discharged....being "fully charged" is way less important.

As long as the battery is allowed to get " fully charged" at least every now and then it should be fine.

AnswerID: 508063

Reply By: Sand Man (SA) - Wednesday, Apr 03, 2013 at 07:34

Wednesday, Apr 03, 2013 at 07:34
The best solution is to use both a solar panel plus a dc-dc charger.
The dc-dc charger will provide the best method of charging your auxiliary battery via the vehicle alternator, providing a multi-stage charging process.

If you invest in a dual alternator/solar input model you will have the best of both worlds.

I use a Ctek D250S Dual dc-dc charger with solar input port and a built-in MPPT solar regulator. This ensures a speedy charging process with the controller able to swap between either input if both sources are active at the same time.

My folding solar panels have a buit-in regulator but it is a very basic one.
I have added a second set of leads which bypass this regulator and when connected to the solar panel input port on the D250S, utilise the MPPT regulator to provide an efficient solar energy source.

The dc-dc charger also boosts the input voltage to overcome any voltage drop in long cable runs and overcomes low voltage levels output by some newer vehicle alternators.

The Ctek D250s Dual is available for $275 from: Kulkyne Campers - D250S Dual


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Reply By: Member - eighty matey - Wednesday, Apr 03, 2013 at 08:30

Wednesday, Apr 03, 2013 at 08:30
Prof Stick,

I bought a 100 watt folding solar panel for about $350 at a 4wd show and it's one of the most valuable items I've ever purchased.

It will easily run our 70 litre Waeco for days, wherever we are, as long as we have sun.

Last year's trip to the Kimberley it saved us a few times because our alternator was playing up and not charging things properly. The solar panel got us out of trouble a few times and without it we would have been stuck miles from anywhere without any help.

AnswerID: 508073

Reply By: Prof Stick - Wednesday, Apr 03, 2013 at 09:41

Wednesday, Apr 03, 2013 at 09:41
Thanks for all the good advice and have read your article Val and it was very helpful. Have provisional approval to get quotes for 80W and 100W panels and submit them to the Expenditure Review Committee by end of week (only cost me a nice home cooked meal and an average bottle of wine). Have decided that we don't need anything bigger because we really only care about the fridge and it only draws 2.5A when running.

Now about the battery. Ours is getting on a bit now, I used to use it as a trolling battery before we bought the fridge. Is there anyway to test it to see how good it is (I have a multimeter but just looking at the voltage doesn't tell you much about its ability to hold a charge and deliver power). If I do decide to replace it what is the best type to get. It WILL be mounted under the bonnet and several people have mentioned that there are types of battery (AGM????) that 'cant stand the heat'. So what is best for under bonnet installation?

Cheers and thanks again for all the help
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